The largely secular climate movement is about to get what some predict will be a historic boost from an intriguing source: Pope Francis.

Francis is putting the final touches on what may be the most authoritative papal teaching ever on the environment, a topic bound up with economics, global development and politics and thus very controversial. Even though no one outside Francis’s inner circle has seen the document — called an encyclical — it’s already being lambasted by some religious and political conservatives and held up by environmentalists as a potential turning point in their movement.

The encyclical is expected to be published in early summer and, church historians say, represents the first time in memory that such an important papal writing is being timed by a pope to influence a civil process — in this case, a major U.N. summit in December on climate change.

Based on remarks and writings by the pope and his close advisers, most pope-watchers think Francis will raise urgent concerns about global warming and highlight human impact on climate change. More broadly, they expect Francis to frame with new emphasis the Earth’s health as a core Catholic social justice concern, up there with topics such as poverty and abortion.

Global inequality and the destruction of the environment “are the greatest threats we face as a human family today,” Cardinal Peter Turkson, a Vatican official who helped write the first draft of the encyclical, said in a March lecture seen as a preview of the document. The pope, Turkson said, “is not making some political comment about the relative merits of capitalism and communism. . . . he is pointing to the ominous signs in nature that suggest that humanity may now have tilled too much and kept too little. ”

Pope Francis arrives for his weekly general audience in St Peter's Square at the Vatican on April 22. (Filippo Monteforte/AFP/Getty Images)

After decades of secular campaigns that failed to move the needle significantly, environmentalists are optimistic about the potential of having religious groups more fully on board in combatting global warming. They have spent years courting skeptical evangelicals, many of whom have begun using the term “creation care.” The recent film “Noah” was seen by many as bringing environmental religion to the big screen, but nothing has been as sweeping as a papal encyclical.

“This has the outreach potential that nothing else has had,” said Mary Evelyn Tucker, co-director of the Forum on Religion and Ecology at Yale University, one of the biggest in a cluster of new groups aimed at connecting faith communities with environmental concerns.

The environmental movement, Tucker said, has been until now largely focused on finding secular solutions in law, science and politics – not ethics and religion. “This is a new moment, when scientists, lawyers and policy people are saying: We need this moral transformation.”

Environmentalism and global warming are not new topics for the Catholic Church. Church leaders — including Pope Benedict — in the last couple decades have been slowly connecting the environmental, moral and economic costs of globalization. However, these connections have never been put forth fully in an encyclical, considered uniquely authoritative in Catholicism.

But it remains to be seen how Francis will link the environment to ethics and theology. That’s where controversy may ensue.

Theologians say he’s likely to place environmental issues into a broader framework he and Benedict have been calling integral ecology, the idea that God wrote a plan for how all living things fit together, a plan that calls for not only less waste, pollution and income disparity but for traditional marriage and sexual mores.

But will Francis vaguely mention sex and family as part of the “integral ecology” or hit it explicitly, as Benedict did? How strongly will he make the case that humans are causing global warming - a case that many Republicans and many conservative Christians don’t buy, think is dangerous to the free market and don’t think a priest - even a pope - is qualified to make? And will he break new theological ground in how he frames care for the environment - describing it not only as a means of helping man (who Genesis says God meant to have “dominion” over other living things) but with value independent of humans?

These are sweeping, controversial questions. And because Francis is a figure not only for Catholics his answers have the potential to impact development and politics way outside the Catholic community.

Also unknown is how, specifically, Francis will urge his church to respond. Will bishops be expected to prioritize the topic in their investments, political efforts, sermons?

Indeed, Catholicism has a big stake in this encyclical. Such documents are considered among the most authoritative teachings of the church, but in recent decades Catholics regularly blow off their mandates on topics like contraception and divorce. Francis’s writing will push the question: How much influence can even this pope have on modern behavior — Catholic and otherwise?

Skeptics have been speaking out for months on both theological and scientific fronts.

Among the most prominent U.S. Christian conservatives is Princeton University Professor Robert George, a Catholic who wrote in the well-respected Christian conservative journal First Things that Catholics are required to follow the pope’s general message on morals — in this case, to care for the environment — but not when he wanders into areas such as scientific fact.

“The Pope has no special knowledge, insight or teaching authority pertaining to matters of empirical fact of the sort investigated by, for example, physicists and biologists..” George wrote in a widely cited article earlier this year. “Pope Francis does not know whether, or to what extent, the climate changes (in various directions) of the past several decades are anthropogenic – and God is not going to tell him.”

Maureen Mullarkey, another First Things writer, put it more bluntly: “He is an ideologue and a meddlesome egoist,” she said, citing Francis’s involvement in the Middle East and US-Cuba relations. “Megalomania sends him galloping into geopolitical – and now meteorological – thickets.”

That’s not as true for more traditional believers, particularly evangelical Christians, who have long been wary of environmentalism, which they worry is Earth-worship that has gone overboard and become essentially its own religion.

Christiana Peppard, a theologian who focuses on environmental ethics at Fordham University, predicted Francis may break ground in potentially two areas.

He will frame environmental concerns other popes have voiced in recent decades in an extremely focused way: how they impact the poor. This could include references to the ways in which woes like poor water quality and weather disasters disproportionately harm the world’s poor. And, Peppard predicted, he may take existing church teaching on the environment, which has always been focused on “effects on the human and the dignity of the human” and possibly posit that the environment “is a gift from God, and that humans have duties to creation as such, not just in light of human concerns.”

These are the areas that have the potential for controversy – how strongly he links human behavior to climate change and whether he sets forth an idea of creation that doesn’t have humans alone at the center.

Chad Pecknold, a theologian at Catholic University, predicted Francis will do neither, particularly the former.

“The moment he would make a strong scientific claim about humans’ role, those Catholics who would dissent from that view would have a claim within the tradition to say the pope has overstepped his bounds,” which would squander a chance to broaden how believers think about the environment, Pecknold said.

He believes Francis will characterize “the human role” in global warming in Biblical terms: That our disconnect with the environment began with Adam and Eve, and the “turning away from our dependence on the order of Creation.” That turning away would include divorce, gay marriage, “and most especially abortion and euthanasia as evidence of a ‘throwaway culture,’” Pecknold said, using a term Francis often says about everything from treatment of the elderly to addicts.

However given Turkson’s and Francis’s previous comments about the human impact on climate change, it seems likely the pope will prescribe both policy and spiritual remedies.

U.S. politics-watchers are anxious to see how top Catholic Republicans from House Speaker John Boehner to potential presidential contenders including Jeb Bush, Rick Santorum and Marco Rubio respond to the encyclical, which will be typically Catholic if it emphasizes as expected major limits to the free market.

Robert Nelson, a University of Maryland economist who focuses on environmentalism and religion, predicted the encyclical “will go over well everywhere except with Republicans.” However, he said, a group that often talks about ethics being too absent from public life could find themselves tempted by a pope putting care for creation back into a traditional framework.

Anthony Annett is a climate change advisor and Catholic writer brought on to the prominent Earth Institute at Columbia University to help bridge the gap between environmentalists and religious communities. Considering Francis chose to name his papacy after the patron saint of animals and the environment and is the most retweeted person on the planet, expectations among environmentalists are soaring.

“I’ve never seen such buzz about a papal document in my life,” he said. “There are a lot of expectations about a document no one has actually seen. And with Francis, expect the unexpected.”